Method for over-pit and under-pit cooperative control of roofs of far and near fields of an extra-large stoping space

ABSTRACT

The invention relates to a control method for a hard roof of a coal mine, specifically to a method for over-pit and under-pit cooperative control of roofs of far and near fields of an extra-large stoping space. The method provided by the invention overcomes the problem of lack of comprehensive and cooperative control methods for hard roofs of far and near fields of an extra-large stoping space in the prior art. According to a technical scheme in the invention, the method comprises an over-pit vertical hole hydraulic fracturing method, an over-pit L-shaped hole hydraulic fracturing method, an over-pit highly-energy-gathered repetition pulse strong shock wave method, an under-pit water injection method, an under-pit layered blasting method and an under-pit hydraulic fracturing method. The method has the advantages that 1) the problem of great mine pressure of the extra-large stoping space is effectively controlled through over-pit and under-pit cooperative control of the hard roofs of far and near fields; 2) advantages of the variety of methods are given to full play and disadvantages of the variety of methods are mutually compensated, so weakening effect on the hard roofs is substantially improved; and 3) all the over-pit and under-pit holes can be used independently or be used in a shared way, so time, manpower, material resources and money used for hole perforation can be greatly reduced.

TECHNICAL FIELD

The present invention relates to a method for controlling a hard roof of a coal mine, and more particularly, to a method for over-pit and under-pit cooperative control of roofs of far and near fields of an extra-large stoping space.

BACKGROUND

With the rapid development of coal industry, the intensive and high-efficient production mode has gradually become a normality of coal mining in recent years. En particular, the application of advanced mining techniques, such as large mining height and higher fully-mechanized mining, leads to a substantial increase in the working face length, the oblique length, the coal seam thickness and the height of roof collapse layer, as well as an abnormal collapse fracturing ratio, which consequently renders an extra-large stoping space and extraordinarily unusual intense pressure during production. In this circumstance, the intense stoping pressure has greatly surpassed the pressure caused by hard basic roof. The destabilized fracture of high hard roof stratum causes more complicated stress field and cover rock spatial structure evolution, large-scale and intensive mining disturbance causes not only the cover rock in caving zone to move tempestuously, but also the spatial equilibrium structure in overlaying goaf to be more destabilized, which consequently causes large-scale abrupt pressure changes in the roof stratum in goaf, even impact ground pressure, coal and gas outburst and other dynamic disasters of coal and gas. The effective pressure reduction is based on not only the control of the hard basic roof of near fields within 30 to 80 meters, but also the control of high hard basic roof of far fields within 100 to 350 meters. Therefore, it is necessary to develop a cooperative roof control method which aims at an extra-large stope and can effectively control the hard roof of near and far fields.

A Chinese patent document CN201510108115.7 discloses “Method and apparatus for weakening high hard roof having distance of 100-350m to coal seam”, which includes the adoption of the method for controlling a hard roof by means of hydraulic fracturing via a vertical bore, hereafter referred to as “the method for controlling a hard roof by means of hydraulic fracturing via a vertical bore”.

A Chinese patent document CN201510037487.5 discloses “Method for decreasing super high seam working face far-field tough roof impact ground pressure strength”, which includes the adoption of the method for controlling a hard roof by means of hydraulic fracturing via an L-shaped bore, hereafter referred to as “the method for controlling a hard roof by means of hydraulic fracturing via a L-shaped bore”.

A further Chinese patent document CN201210013370.x discloses “Method for controlling rock burst by pulse fracturing”, which includes the adoption of the method for controlling a hard roof via strong repeating impact pulse of high energy density, hereafter referred to as “the method for controlling a hard roof via strong repeating impact pulse of high energy density”.

A further Chinese patent document CN201210144077.7 discloses “Stratified blasting method for coal mine hard roof”, which includes the adoption of the method for controlling a hard roof via stratified blasting, hereafter referred to as “the method for controlling a hard roof via stratified blasting”.

A Chinese patent document CN201310483719.0 discloses “Method for increasing top-coal recovery rate in primary mining period of fully-mechanized caving face”, which includes the adoption of the method for controlling a hard roof via weakening by hydraulic fracturing, hereafter referred to as “the method for controlling a hard roof via weakening by hydraulic fracturing”.

SUMMARY OF THE INvENTION

The present invention aims at solving the problem of lacking comprehensive and cooperative hard roof control method for near and far field of an extra-large stoping space and provides a method for over-pit and under-pit cooperative control of roofs of far and near fields of an extra-large stoping space.

The present invention is realized by following technical solution: a method for over-pit and under-pit cooperative control of roofs of far and near fields of an extra-large stoping space includes a method for controlling a hard roof by means of hydraulic fracturing via an over-pit vertical bore of far field of an extra-large stoping space, a method for controlling a hard roof by means of hydraulic fracturing via an over-pit L-shaped bore of far field of an extra-large stoping space, a method for controlling a hard roof via an over-pit strong repeating impact pulse of high energy density of far field of an extra-large stoping space, a method for controlling a hard roof via down-pit water injection of near field of an extra-large stoping space, a method for controlling a hard roof via down-pit stratified blasting of near field of an extra-large stoping space, and a method for controlling a hard roof via weakening by hydraulic fracturing of near field of an extra-large stoping space;

wherein firstly the hard roof of far field is controlled by adopting the method for controlling a hard roof by means of hydraulic fracturing via an over-pit vertical bore of far field of an extra-large stoping space;

secondly, the hard roof of each target stratum is controlled by adopting the method for controlling a hard roof by means of hydraulic fracturing via an over-pit L-shaped bore of far field of an extra-large stoping space;

then, the weakened hard roof of each target stratum is further controlled by adopting the method for controlling a hard roof via an over-pit strong repeating impact pulse of high energy density of far field of an extra-large stoping space;

so far, the over-pit constructive control of the hard roof of far field of an extra-large stoping space has been completed, simultaneously or successively, the down-pit constructive control of the hard roof of near field of an extra-large stoping space is conducted, firstly, the near-field hard roof is preliminary controlled by adopting the method for controlling a hard roof via down-pit water injection of near field of an extra-large stoping space;

then, the near-field hard roof is controlled and weakened in layers by adopting the method for controlling a hard roof via down-pit stratified blasting of near field of an extra-large stoping space;

finally, the near-field hard roof is controlled by adopting the method for controlling a hard roof via weakening by hydraulic fracturing of near field of an extra-large stoping space.

A control of the far-field hard roof is realized by successively adopting over-pit vertical bore hydraulic fracturing method, over-pit L-shaped bore hydraulic fracturing method, over-pit strong repeating impact pulse of high energy density method, wherein the proper construction order of the above three methods not only maximizes their individual advantages, but also greatly strengthens their co-actions, which can be embodied as: 1) The vertical bore hydraulic fracturing method is firstly adopted to intensively weaken a part of the far-field hard roof, but it has the defects of limited coverage, usually about several tens of meters in radius, for far-field hard roof of an extra-large stoping space, if vertical bore hydraulic fracturing method is adopted exclusively, multiple vertical bores are needed on the vast mining face, which consumes paramount human resource, material and money; 2) The L-shaped bore hydraulic fracturing method focuses on weakening far-field hard roof of the same target strata, as the L-shaped bore can function within a larger coverage, it effectively makes up the defects of vertical bore hydraulic fracturing method; 3. Strong repeating impact pulse of high energy density hard roof control method is adopted to thoroughly weaken the hard roof of each part and each strata after the preliminary weakening by vertical bore and L-shaped bore hydraulic fracturing.

Meanwhile, the over-pit control methods can only weaken the far-field hard roof, while the near-field hard roof control must be controlled down-pit by successively adopting down-pit water injection method, down-pit stratified blasting method, and down-pit hydraulic fracturing method. Again, the proper construction order of the above three methods not only maximize their individual advantages, but also greatly strengthen their co-actions, which can be embodied as: 1) Firstly, moisten and weaken the near field hard roof by adopting down-pit water injection method, so as to strengthen the effects of the subsequent control methods, which is a conventional technical scheme in this field. But the weakening effect caused by down-pit water injection method on hard roof is limited by its injected moisture radius. Similar to the over-pit vertical bore hydraulic fracturing method, if the weakening of extensive mining face is required, it requires of multiple water injection bores, into which plentiful dynamic and static pressure water must be injected. While the near field hard roof is weakened, the pressure of the roof is also increased, which brings about safety hidden perils; 2) The down-pit stratified blasting method is aimed for the weakening of the hard roof in the same target strata, which enables the wedge groove pre-splitting crack to defuse outwards after the blast, after the near-field hard roof being preliminary weakened through water injection, the diffuseness of pre-splitting crack raises substantially than before; 3) After the near-field hard roof being preliminary weakened through moistening, further weakening through blasting, the adoption of down-pit hydraulic fracturing method can thoroughly weaken the hard roof at each target strata and in each space, whose weakening effect is significantly enhanced compared to that of independent adoption. As the far-field over-pit hard roof control method and the near-field down-pit hard roof control are mutually non-interfered, they can be processed simultaneously and successively.

The present invention has following advantages: 1) The over-pit and down-pit cooperatively control the hard roof of near and far fields, which effectively brings the strong pressure in extra-large stoping space under control; 2) The advantages of various methods are effected fully and the disadvantages of every means are compensated, which greatly improves the weakening effects of hard roof; and 3) The bores in over-pit and down-pit can used independently and cooperatively, which significantly reduces the cost of time, human resources, materials and money.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is the schematic constructional view of the far-field over-pit vertical bore hydraulic fracturing hard roof control method for extra-large stoping space and the far-field over-pit L-shaped bore hydraulic fracturing hard roof control method for extra-large stoping space.

FIG. 2 is the schematic structural view of blast bore and hydraulic fracturing bore;

LIST OF REFERENCE MARKS

1-L—shaped bore, 2—vertical bore, 3—perforating slots, 4—ground, 5—far-field hard roof, 6—near-field hard roof, 7—working face, 8—blast bore, 9—hydro-fracturing bores, 10—wedge pre-splitting crack.

DETAILED DESCRIPTION

The method for over-pit and under-pit cooperative control of a roofs of far and near fields of an extra-large stoping space includes a method for controlling a hard roof by means of hydraulic fracturing via an over-pit vertical bore of far field of an extra-large stoping space, a method for controlling a hard roof by means of hydraulic fracturing via an over-pit L-shaped bore of far field of an extra-large stoping space, a method for controlling a hard roof via an over-pit strong repeating impact pulse of high energy density of far field of an extra-large stoping space, a method for controlling a hard roof via down-pit water injection of near field of an extra-large stoping space, a method for controlling a hard roof via down-pit stratified blasting of near field of an extra-large stoping space, and a method for controlling a hard roof via weakening by hydraulic fracturing of near field of an extra-large stoping space;

firstly, the hard roof of far field is controlled by adopting the method for controlling a hard roof by means of hydraulic fracturing via an over-pit vertical bore of far field of an extra-large stoping space, which specifically includes the following steps:

a. drilling a vertical hydraulic-fracturing bore 2 from the ground 4 towards the far-field hard roof 5 overlying a working face 7, with the distance from the end of the fracturing bore to the working face being 100-350 m;

b. injecting fracturing fluid from a fracturing string into the vertical hydraulic-fracturing bore 2 and a guidance fracturing bore by means of a high pressure water perforator and a fracturing device, and slotting the stratum of the far-field hard roof 5 via a perforator gun;

c. after the formation of perforating slots 3 by perforating the target stratum, continuing to inject the fracturing fluid from the fracturing string, and simultaneously injecting proppant into the annulus between the fracturing string and a sleeve to finish the hydraulic fracturing work of vertical hydraulic-fracturing bore 2, after which performing a reverse circulation purge via a perforated tube and a check valve, and then lifting the fracturing string to conduct the work of the next target stratum; after the completion of this work of all the target strata, lifting the fracturing string from the sleeve out of the fracturing bore.

secondly, the hard roof of each target stratum is controlled by adopting the method for controlling a hard roof by means of hydraulic fracturing via an over-pit L-shaped bore of far field of an extra-large stoping space, which specifically includes the following steps:

d. drilling an L-shaped hydraulic-fracture bore 1 from the ground 4 towards the far-field hard roof 5 overlying the working face 7, with the vertical distance from the horizontal bore to the working face 7 being 100-350 m;

e. injecting fracturing fluid into the L-shaped hydraulic-fracturing bore 1 from a fracturing string by means of a high pressure water perforator and a fracturing device, and perforating and slotting the stratum of the hard roof at high level via a perforator gun;

f. after the formation of perforating slots 3 by perforating the target stratum in segments, continuing to inject fracturing fluid from a fracturing string, and simultaneously injecting proppant into the annulus between the fracturing string and a sleeve to finish the hydraulic fracturing work of the target stratum having horizontal bore in segments via the L-shaped hydraulic-fracturing bore; after the completion of this work, lifting the fracturing string from the sleeve out of the fracturing bore;

then, the weakened hard roof of each target stratum is further controlled by adopting the method for controlling a hard roof via an over-pit strong repeating impact pulse of high energy density of far field of an extra-large stoping space, which specifically includes the following steps:

g. drilling a vertical impact bore from the ground 4 towards the far-field hard roof 5 overlying the working face 7, with the vertical distance from the end of the vertical impact bore to the working face being 100-350 m;

h. injecting clean water into the vertical impact bore until it is saturated;

i. inserting the probe of strong repeating impact pulse generator into the vertical impact bore, and submerging it into the clean water; energizing the probe of strong repeating impact pulse generator, so that it can create impulsed high-voltage discharge towards the target stratum of the hard roof at high level, so as to form a crack and widen it to finish the impact and weakening work of the target stratum at the vertical bore via strong repeating impact pulse of high energy density; after the completion of this work, lifting the probe of strong repeating impact pulse generator from the vertical bore out of the impact bore;

so far, the over-pit constructive control of the hard roof of far field of an extra-large stoping space has been completed, simultaneously or successively, the down-pit constructive control of the hard roof of near field of an extra-large stoping space is conducted; firstly, the near-field hard roof is preliminary controlled by adopting the method for controlling a hard roof via down-pit water injection of near field of an extra-large stoping space, which specifically includes the following steps:

j. forming a plurality of water injection bores at down-pit space towards the near-field hard roof 6 overlying the working face 7, and injecting cement slurry into the ports of the individual water injection bores to seal the bores;

k. injecting dynamic and static pressure water into the water injection bores via the high-pressure water injection pump, with the quantity of the injected water being determined by an empirical moistening radius;

l. repeating the above steps to inject water into each water injection bores, so as to complete the preliminary softening work of the near-field hard roof 6.

then, the near-field hard roof is controlled and weakened in layers by adopting the method for controlling a hard roof via down-pit stratified blasting of near field of an extra-large stoping space, which specifically includes the following steps:

m. forming a plurality of blasting bores 8 at down-pit space towards the near field hard roof 6 overlying the working face 7, and drill a pre-crack 10 in the form of a wedge-shaped groove in each of the blasting segments along each blasting bore 8;

n. placing the primary explosive, taphole clay and wooden wedge into the blasting segment of the blasting bore 8 in sequence, clamping the wooden wedge tightly to complete the loading of the first blasting segment in the blasting bore 8, and then repeating the above steps to complete the loading of all the blasting segments;

o. repeating the above steps to complete the loading of all the blasting bores, sealing all the blasting bores with taphole clay, and then connecting a detonator to a detonating cord and stemming; at last, connecting the blasting network to initiate the blast;

finally, the near-field hard roof is controlled by adopting the method for controlling a hard roof via weakening by hydraulic fracturing of near field of an extra-large stoping space, which specifically includes the following steps:

p. forming a plurality of hydraulic fracturing bores 9 at down-pit space towards the near-field hard roof 6 overlying the working face 7, and drill a pre-crack 10 in the form of a wedge-shaped groove in each of the fracturing segments along the drilled bore;

q. pushing a bore packer having a hydraulic-fracturing mounting bar into the hydraulic fracturing segment, and pressurizing the bore packer to seal the hydraulic fracturing segment;

r. injecting high-pressure water into the hydraulic fracturing bore via fracturing pump to fracture the hydraulic fracturing segment;

s. as each hydraulic fracturing bore has a plurality of hydraulic fracturing segments, repeating the above steps to conduct the fracturing work in segments and complete the work of all the hydraulic fracturing segments of each hydraulic fracturing bore. 

1. A method for over-pit and under-pit cooperative control of roofs of far and near fields of an extra-large stoping space, including a method for controlling a hard roof by means of hydraulic fracturing via an over-pit vertical bore of a far field of an extra-large stoping space, a method for controlling a hard roof by means of hydraulic fracturing via an over-pit L-shaped bore of a far field of an extra-large stoping space, a method for controlling a hard roof via an over-pit strong repeating impact pulse of high energy density of a far field of an extra-large stoping space, a method for controlling a hard roof via down-pit water injection of a near field of an extra-large stoping space, a method for controlling a hard roof via down-pit stratified blasting of a near field of an extra-large stoping space, and a method for controlling a hard roof via weakening by hydraulic fracturing of a near field of an extra-large stoping space; characterized in that the method comprises following steps: firstly, the hard roof of the far field is controlled by adopting the method for controlling a hard roof by means of hydraulic fracturing via an over-pit vertical bore of a far field of an extra-large stoping space; secondly, the hard roof of each target stratum is controlled by adopting the method for controlling a hard roof by means of hydraulic fracturing via an over-pit L-shaped bore of a far field of an extra-large stoping space; then, the weakened hard roof of each target stratum is further controlled by adopting the method for controlling a hard roof via an over-pit strong repeating impact pulse of high energy density of a far field of an extra-large stoping space; so far, the over-pit constructive control of the hard roof of the far field of the extra-large stoping space has been completed, simultaneously or successively, the down-pit constructive control of the hard roof of the near field of the extra-large stoping space is conducted, firstly, the near-field hard roof is preliminary controlled by adopting the method for controlling a hard roof via down-pit water injection of a near field of an extra-large stoping space; then, the near-field hard roof is controlled and weakened in layers by adopting the method for controlling a hard roof via down-pit stratified blasting of a near field of an extra-large stoping space; finally, the near-field hard roof is controlled by adopting the method for controlling a hard roof via weakening by hydraulic fracturing of a near field of an extra-large stoping space. 